Multi-speed transmissions of the type utilized in heavy road vehicles generally are composed of a multi-speed transmission section, a range section and a splitter gear or overdrive section. One ratio in the multi-speed section may be used only in the low range as a starting gear while the remaining four ratios are each used first with the low range and then with the high range section. While in the high range section the four ratios utilized can be further "split" by the overdrive. That is each gear can first be engaged with the "direct" drive and then with the "overdrive" range.
In order to accomplish this, the transmission control available to the operator usually includes a shifting cane for operating the multi-speed transmission and an auxiliary control for shifting from low range to high range and while in the high range for shifting from direct to overdrive. It is to be understood that all multi-speed transmissions of the type envisioned have required a clutch, however the clutch or operation thereof is not pertinent to this invention. In the past various valving schemes have been provided for fixture to the shifting cane however all have suffered one or more drawbacks.
In one instance the low-high range valve is separately mounted below the end of the shifting cane thus necessitating either removing the hand from the knob and the end of the shifting cane or utilizing the other hand to shift from low to high range.
In another scheme illustrated in part in U.S. Pat. No. 3,979,967 a flat head is placed on the end of shifting cane with a thumb operated lever projecting radially outwardly from the flat head. The thumb operated lever is movable between three positions namely the low range position, the high range or direct position and the overdrive position. During highway operation shift between direct and overdrive may occur rather frequently and is accomplished by the operator's thumb. The aforementioned patent teaches a modification to the shifting cane to facilitate movement between the direct and overdrive position.
Nevertheless the conventional valving structure mounted on the end of the shifting cane and illustrated in the aforementioned patent even while so modified becomes burdensome to operate and in some instances, the operator's thumb may become pinched between the housing and the thumb operated lever.
It is most important that the operator have a convenient, easily operated safe valve at his immediate beck and call since shifting a transmission of a road operated vehicle is most important. Such shifting is necessary in order to maintain the speed of the driving engine within an acceptable range. This is required because of the use of an internal combustion compression ignition engine which operates best in a narrow engine speed range rather than a wide range of speeds.